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Capacitor on input pin

Question asked by Dirk Schäfer on Feb 28, 2017
Latest reply on Feb 28, 2017 by igorpadykov

Dear all,

 

I connect the collector of an opto-coupler, ACPL-847-300E, with one PIN of the iMX6, PIN configured as GPIO inport, Schmitt-trigger, slow, 22kOhm. That works fine, inverted logic.

Now I placed a 3.3nF capacitor to that PIN, hoping to control the frequency, 1/2*PI*R*C, by the PIN control register.

But the behavior is not like expected. Falling edges lead to one edge, but rising edges lead to more then one rising-falling edge. Like the signal bounces around the threshold of being 1 or 0.

 

The put the filter in the entrance of the opto-coupler is more likley, I think. But the possibility to change the cutoff frequency would be nice.

Is it impossible, or would I need more then a capacitor?

 

Many thanks for your help.

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